2.3. TYPES OF WHEELS
Two principal types of wheels are in general use in the United States today: cast-steel and wrought-steel.
While the Army still has some cast-iron wheels on equipment used only on the utility railroads inside
installations, their use in the interchange service in the United States ended in 1967.
Both steel wheels are one-wear, two-wear, or multiple-wear, designating the number of times the rim,
after wearing off, can be restored to its original flange contour. In the one-wear wheel, once the flange or tread
is worn to the condemning limits, the rim thickness is not great enough to permit any restoring; the two-wear
wheel can be restored once and the multiple-wear several times until the condemning limit of the one-wear
wheel is reached. The two main points discussed in this section are how to detect wheel defects and how to
determine wear limits. First, however, two paragraphs describe briefly the wheels themselves and the processes
of manufacturing that conform to the Association of American Railroads (AAR) specifications for foundry
practice, inspections, tests, and records.
2.4. CAST-STEEL WHEEL
Used only for freight cars, cast-steel wheels are made of steel melted in electric furnaces. Wheels fall into
one of five classes:
Class U--untreated; for general service where an untreated wheel is satisfactory.
Class A--treated; for high-speed service with severe braking conditions but with moderate wheel loads.
Class B--treated; for high-speed service with severe braking conditions and heavier wheel loads.
Class C (l)--treated; for service with light braking conditions and high wheel loads.
(2)--treated; for service with heavier braking conditions where off-tread brakes are used.
The heat treatment for classes A, B, and C wheels includes treatment of the rim only. Wheels are reheated
uniformly to refine the grain and then the rims are quenched. After quenching, wheels